Study Analyzes Climate Change Impact on Feds' Hydro System

by Mike O'Bryant
Columbia Basin Bulletin - December 13, 2002

Working with University of Washington climate change experts, the Northwest Power Planning Council is midway through a study on how the projected warming of the region's climate would impact the federal Columbia River hydroelectric system and salmon restoration efforts.

Council staff is working from a recently published study in the journal Climatic Change that looked at the impacts of global warming on western state river systems and with researchers in the Department of Civil and Environmental Engineering at the University of Washington, who contributed Columbia River Basin information to that report. The report found that average air temperatures will increase and the water content of the Northwest's snow pack in April will decline by up to 50 percent by the end of this century, leaving less stream flows in summer and autumn for power production and juvenile and adult salmon migration.

John Fazio, Council staff, ticking off a list of those impacts to the hydro system in his presentation to the full Council at its Portland meeting this week, said that by 2020 the region can expect a 2 degree Fahrenheit increase in average temperatures, a decline in May and June peak flows and an overall decline in summer flows. That will be offset by higher river flows in late fall and winter as more precipitation falls as rain rather than as snow. However, the shift to an earlier snow pack runoff will dramatically impact flows now reserved for salmon migration.

"Peak runoff will come about a half month early," Fazio said. "But, we will get higher winter flows." He added that the Bonneville Power Administration's winter loss of load probability will actually improve from 8.6 percent to 7.3 percent and the federal power system will see a net gain in power production of about 500 average megawatts. However, the period when that electricity will be generated will change. "We'll see higher generation in the winter, but lower generation in the spring and summer months," he said.

That may hurt BPA revenues because the agency counts on secondary summer sales to enhance its annual revenue, said Council Chair Larry Cassidy of Washington.

On the other hand, the change in spring and summer flows caused by a smaller and earlier snowmelt will impact flows now used to protect salmon, including the system's ability to provide enough water for spill. For one thing, Fazio said, it will be more difficult to refill Libby Dam in Montana, a headwater storage project important for providing flows lower in the river. Lettenmaier said that Canadian headwater dams will see less of a change because snow pack in Canada will not be affected as much.

Climate change will also impact the probability of meeting in-stream flow targets at McNary Dam, but not by much, largely because the flow targets are met only about half the time now, Lettenmaier said. However, when the target is missed, it will be missed by a larger margin, he said, and that could be a liability for agricultural interests.

Both Lettenmaier and Fazio suggested that altering spring flood control rule curves could provide more stored water, but not a lot. Also, a decision would have to be made whether to use the stored water for fish flows or for generation, although it helps only a little in both cases. Lettenmaier found that early refill of projects isn't a very effective alternative. "The only thing that seems to make a difference is to save more storage for fish, but that comes out of the hide of hydropower," he said.

The region could arrange with Canada to provide more water from storage, or it could lower draft limits at storage dams, Fazio said. "But, that leaves you heading into next year with an empty gas tank," he said, creating even larger problems.

Cassidy said another alternative would be to build more storage projects, pointing to projects proposed in the Yakima River Basin. That, said Fazio, would put more gas in the tank to get the hydro system through low spring and summer flows.

At the least, the region should "re-optimize" flood control rule curves, especially at Libby and Dworshak dams and re-examine fish and wildlife operations in light of global warming, Fazio said.

The results Fazio has gotten so far from his study is very close to that completed by Lettenmaier and his colleagues in November, which predicted temperature and rainfall changes during three consecutive periods this century, projecting a 1.3 degree Centigrade increase in average temperature during the period 2040 to 2069, and an increase in winter precipitation during that period of 5 percent. However, by then, much of the winter precipitation will fall as rain and will not contribute to the winter snow pack. Fazio's study, which will be used in the Council's upcoming power plan, looks at the impacts through 2020.

"It's clear that at some point we will have to go with emissions controls," Lettenmaier said, warning he is a scientist, not a policy expert. "The question is how much and when?" However, even if the world goes with controls now, it may take a couple of decades to reverse the warming trends occurring today.